1. Field of the Invention
The present invention pertains to a well conduit (tubing and/or casing) cutting and milling apparatus and method for insertion in a wellbore to cut through a tubing or casing section and to mill out a predetermined length of tubing or casing.
2. Background
In subterranean well operations, it is occasionally necessary to cut and remove a section of a tubing string or well casing. To this end, several configurations of tubing or casing cutting and milling tools have been developed for use with conventional drill rigs which must be brought on site over the well head. However, the cost and time consumed in using conventional rigs is disadvantageous and there has been a significant increase in the use of so-called coiled tubing units for certain well operations.
Basically, known prior art types of cutting and milling tools for use with conventional drill rigs are configured for cutting through a tubing or casing section and then mill away a portion of that section by moving the tool in a generally downward direction. The operation of these types of tools has several shortcomings when attempted to be used with coiled tubing. Control over the axial downward pressure on the tool is usually difficult to maintain because of the flexibility of the tubing string to which the tool is connected. Accordingly, the cutting or milling tool may wear prematurely and the downward pressure may also deflect the casing or tubing being cut resulting in failure of the tool and/or the tubing or jamming of the tool in the casing or tubing.
Known types of casing, cutting and milling tools are also not adapted to being inserted into the casing string through smaller diameter tubing strings. Known types of tools require removal of the tubing string from the wellbore before the tool can be inserted and operated to cut and mill away a section of casing.
Still further, known types of tools are difficult to operate when cutting and milling tubing since, in many instances, the tubing string may be forced "off center" with respect to the central axis of a casing or larger diameter tubing string in which the tubing string to be cut and milled is located. Still further, known types of cutting and milling tools are sometimes unduly complicated, are otherwise difficult to use, particularly when replacement of the cutter or milling members is required.